An x-ray cassette for the accommodation of photosensitive material in sheet form, especially an excitable phosphor sheet, comprises a cover part, a bottom part and side parts joined thereto. The cover part, bottom part and side parts are made of plastic and enclose the cassette interior in a light-tight manner.
An x-ray cassette of this kind is disclosed, for example, in German Patent Publication No. OS 30 43 070 A1. The cassette therein described serves to contain an x-ray film. A film inserted therein is enveloped in a light-tight manner by a cover, a bottom and side parts made of plastic. Image intensifier sheets are provided adjacent to the x-ray film, on at least one of the two halves of the cassette, which convert the x-rays to visible light and expose the x-ray film. The x-ray film is exposed both by an image intensifier on the cover side and by another one on the bottom side.
The x-ray cassette is automatically loaded and unloaded under darkroom conditions. For this purpose various types of apparatus are already known, for example as disclosed in the German Patent No. 36 10 660 C1. An x-ray film cassette to be loaded or unloaded is inserted into the apparatus therein described, opened under light-tight conditions, and the film is removed from the cassette by a suction device. The cassette is then reloaded with a fresh, unexposed film of a size fitting the cassette, and the cassette is reclosed and dispensed at the front of the apparatus.
For some time processes have also been known in which excitable phosphorus screens are used and exposed to the x-radiation, in place of the conventional x-ray film and intensifying screen. For this purpose various kinds of cassettes are employed, which are of a construction very similar to those used for x-ray photographs with x-ray films. A cassette for excitable phosphor screens and a method of using it is described, for example, in the German Patent Publication No. OS 37 31 203 A1. In the method used with this cassette the screen is removed from the cassette after x-ray exposure, made to luminesce by means of a laser beam scanner, and the light emitted is converted to digital electronic image signals. The image information is then erased on the film by exposing it to appropriate radiation. The digital image signals are stored in a central memory and subjected to digital image processing in which, for example, certain image information can be filtered out. The picture can then be displayed by a peripheral device (video monitor, printer or film reader). In the case of x-ray photography, both with x-ray film and with excitable phosphor sheets, the problem often arises that, when the cassette is loaded or unloaded, dust enters the cassette interior and collects in the cassette. These grains of dust can result in damage to the film or sheet and can also produce unwanted images on film or sheet. Such artifacts are undesirable especially in medical diagnosis when the x-ray images are evaluated.